Frequently it is desirable to separate out one or more components that are useful from a fluid mixture that contains other components that may not be useful or are less valuable or less useful. To accomplish this it is often necessary or desirable to fractionate such a fluid mixture to separate out the useful or desired components. This has been accomplished through the use of liquid chromatography systems. Unfortunately, previous liquid chromatography systems have a number of problems or disadvantages.
One of these problems is related to fluid control. In this connection, the control of fluid flow is of primary importance in the field of liquid chromatography. In a liquid chromatography system a fluid, usually comprising a carrier fluid and a sample fluid, is injected into a separation column, as the fluid passes through the column the constituents of the sample fluid travel at different velocities due to their various rates of interaction with the packing material of the column. The result of this procedure is an output flow of the various individual constituents one after the other and consequently the output of the column would initially contain only the least retained constituent and etc. Ideally, there would be a sharp cut off at the interface between constituents. However, in practice this has not always been the case and the transition from one constituent of the sample fluid to the next is often gradual and indistinct resulting in inefficient separation of the constituents.
This transition problem between constituents can result from the fact that, in many columns, the fluid flow along the column is usually confined to a core portion of the column-packing material. The inefficiency arises because the core segment quickly becomes saturated and constituents which should be slowed after traveling a certain length along the columns continue to flow since they cannot interact with the saturated packing material of the core segment. Thus the output of the constituents at the transitions are blended and indistinct. The capacity of the column for increased loads of the sample constituents is also significantly reduced since only the core portion of the packing material is being utilized.
The constrained fluid flow through a liquid chromatography column also reduces the useful life of that column. The useful life of a given packing material is finite since, when a fluid is passed over the packing material a small amount of the constituents of that fluid may be irreversibly retained. Consequently, for a given cross-section of packing material if all the fluid passed is confined to a core segment the useful life of that cross-section of material is less than if the same amount of fluid were distributed across the entire cross-section.
Another problem associated with column chromatography is the inability to readily scale up the size of usable systems. Column chromatography has become an accepted conventional laboratory method for use in the separation of materials. However, when attempts are made to use this method on a large scale, a number of difficulties arise which have previously rendered the practicability of large scale column chromatography questionable. Particularly serious difficulties arise with increasing length and diameter of the columns, by the distortion of the fronts between constituents which leads to a poor utilization of the column capacity, and, especially in the case of low separation factors, to the impossibility of adaptation to large scale separation of the multi-component liquid.
The distortion of the fronts is due to a great variety of different factors, such as nonuniform filling of the column and fluid distribution, variations in temperature, viscosity and volume, channel formation, and the like. Thus, whereas in the ideal case, the concentration time diagram of a liquid which has passed through a chromatographic column represents a more or less steep bell-shaped curve, in the case of columns used for large scale chromatography, this diagram degenerates into drawn out shapes.
There have also been problems associated with filling the column chromatography unit with packing material and removing bubbles of air and other gasses from liquid in the column. In this connection, in a fixed length column it is very difficult to properly pack the column with just the right amount of packing material and an incorrectly packed column can prevent the proper separation of the constituents passing through the column. Although the length of the column has been allowed to be varied by the use of a variable position end such as a plunger, there have been problems associated with its proper use. It has also been difficult to remove bubbles from the liquid that is introduced into a packed column and the presence of bubbles can interfere with the proper operation of the column.
This invention overcomes these previous problems associated with column chromatography and provides for the proper control of liquid flow for the effective separation of the constituents, provides an effective plunger, allows the unit to be increased in size without loss of effectiveness and allows gas bubbles to be effectively removed from liquid in the column.